Key Items in Devil May Cry 4

Proud Soul
The Proud Soul is obtained after completing a mission, and the amount of Proud Souls obtained is dependent on the rank received in the mission. It is a manifest soul that is filled with pride due to its noble blood, and is used to purchase new abilities from a Divinity Statue.

Evil Legacy
The Evil Legacy (負の遺産) is found within a blue pillar in the Cathedral of Mission 2. It is a special crystal that holds the power of an ancient evil, and after being absorbed into the Devil Bringer, it grants Nero the ability to perform Snatch by locking onto small enemies, or Hell Bound by locking onto Grim Grips and large enemies. Many Grim Grips require Nero to step upon a blue Continuum Pad to become activated, though there are more that do not. Once obtained, Snatch can be used during any mission, including those "before" it was found.

Anima Mercury
The Anima Mercury (水銀のアニマ) is found within a yellow pillar in the Library of Mission 3. It is an artificial soul made through alchemy that can be used to animate Gyro Blades. Nero can move a Gyro Blade by using Buster near it, and can speed it up by striking it with his sword before moving it with another Buster. Animated Gyro Blades can be used to destroy barriers and objects or shred enemies.

Rusalka Corpse
The Rusalka Corpse (ルサルカの亡骸) is one of Bael's feelers, obtained after Nero rips it off his head in Mission 4. After being absorbed by the Devil Bringer, it grants Nero the Auto-Search ability. When near hidden Red Orbs, Blue Orb Fragments, or Secret Missions, the Devil Bringer will begin glowing, strengthening as it gets nearer to the hidden object. However, the glow is not visible while charging a Charged Shot. Once obtained, Auto-Search can be used during any mission, including those "before" it was found.

Sephirothic Fruit
The Sephirothic Fruit (セフィロトの実) is one of Echidna's seeds, obtained after it falls from her as she flees at the end of Mission 7. After being absorbed by the Devil Bringer, it grants Nero the ability to wither certain demonic trees that entangle areas of Mitis Forest and in the Order of the Sword HQ.

Aegis Shield
The Aegis Shield (アイギスの楯) is Angelo Credo's shield, obtained after Nero defeats him in Mission 8. After being absorbed by the Devil Bringer it grants Nero the ability to perform Hold. Once obtained, Hold can be used during any mission, including those "before" it was found.

Wing Talisman
The Wing Talisman (羽のタリスマン) is found within a red pillar in the Spiral Well during Mission 5. It is a crystal talisman containing an angel's wing that can be used to activate certain equipment which will propel Nero or Dante upwards if stepped upon. These pads are usually red, though there are some blue ones that effect a much greater response. There is also an elevator within Experiment Disposal which requires the Wing Talisman to be placed inside of it to move, and Nero does so while searching the H.Q. for Kyrie. Dante later retrieves the talisman in Mission 12.

Key of Cronus
The Key of Cronus (クロノスの鍵) is found by Nero in Mission 9 within a violet pillar in the Key Chamber. It is a magical key intended for use with the Chrono Slicers, time suspension devices being developed by the Order's technology department. Most of them are incomplete and will only remain active for a short time. However, there is one Chrono Slicer within the Security Corridor which functions indefinitely if the key is left inside, and Nero does so while searching the H.Q. for Kyrie. Dante later retrieves the key during Mission 12, and uses it to wreck some of the machines in the Security Corridor.